1. Field of the Invention
The present invention relates to a display apparatus employing matrix electrodes and, more particularly, to a liquid crystal display apparatus which employs ferroelectric liquid crystal and performs scanning for partial rewriting.
2. Description of the Related Art
A liquid crystal display device for displaying image information is known which comprises many pixels formed by placing a liquid crystal compound between an array of scanning electrodes and an array of signal electrodes to constitutes a matrix of electrodes. An example of this type of display device is illustrated in Figs, 15 and 16. A scanning method used in such a display device is disclosed, for example, in U.S. Pat. No. 4,655,561 (Kanbe et al.) and in U.S. Ser. No. 85,017 (Inoue et al., Aug. 13, 1987). The method utilizes a memory to scan for partial rewriting so as to maintain a smooth display of movements even during low field frequency scanning.
Another driving waveform is disclosed by Taniguchi et al. in European Laid-Open No. 394,903, which helps to speed up the frame frequency and provide a sufficient driving margin, i.e., the range of the driving voltage or the writing pulse width within which images of favorable quality can be displayed.
However, since the scanning waveform according to the above conventional art is a black erasing waveform and includes DC components, frequent repetition of partial-rewrite scanning on a single scanning electrode causes the following problems in the pixels on that scanning electrode.
(1) decrease of the driving margin
(2) deterioration of liquid crystal alignment
(3) decrease in sharpness of contrast